I also examined the following case:
WebUI.takeFullPageScreenshot(RunConfiguration.getReportFolder() + '/foo.png')
In this case, the foo.png was found attached into the Basic Report.
So, I was not correct in saying “the png will be included in the Basic Report if you specify NO local file path as argument to the keyword”. If you saved the png in the Reports directory with any file name, the Basic Report seems to be able to render the png.
I guess, the design of the program that compiles “Basic Report” matters. The reporting program seems to be assuming that the PNG files should be saved in the reports directory. If the PNG file is saved somewhere outside the assumed reports directory, then it can not include the PNG into the report html.
Well, I think this design is understandable; acceptable if properly documented.
However, it is a shame, the Basic Report has no official documentation. Therefore @cyntiaverolita was puzzled. @cyntiaverolita needs to find out how the system works by experiments as I did.